Power Loss in GK Heads

I was reading through one of the GK threads and someone mentioned that GK heads have had documented problems with the power supply.

Does anyone have any information on this?

I run a GK 800RB through a Hartke 4x10 Transporter. Every once in a while I would notice that turning up would not give me the appropriate volume. And then after playing a bit, the volume would kick in and I'd be way too loud. I'd turn it down and start the cycle again. Now it's happening a lot more frequently.